In a storage system in which a plurality of servers (hereinafter, referred to as hosts) share one storage apparatus, there are cases where input/output processes requested from the hosts contend inside the storage apparatus, and stable performance is not be maintained for each input/output process (application). Thus, there are cases where a storage apparatus has a quality of service (QoS) function for maintaining appropriate performance according to a priority level for each input/output process by performing the process with priority levels (degree of priority) being assigned to the processing requests from the hosts.
Relating to the QoS function (storage QoS) included in a storage apparatus, a technology for allocating internal resources such as a queue and the like based on a priority level designated by a host and executing a command is known. As an example, a case will be described in which, in a storage system in which two hosts A and B share one storage apparatus, host A transmits a command with a priority level being designated thereto. When the priority level is designated from host A, for example, the storage apparatus allocates internal resources that are three times those allocated to a process to which a priority level is not designated. As a result, the storage apparatus performs an input/output process requested from host A with priority over an input/output process requested from host B.
In addition, a technology for maintaining appropriate performance according to a priority level for each input/output process (application) by setting target performance or a bandwidth limit to each host or logical unit (LU) on the storage apparatus side is known.
Furthermore, a technology for responding to a change in the load status by changing a priority level set for a specific input/output process in a case where the load status of the input/output process changes is known. For example, according to such a technology, in a case where an actual input/output processing amount is continuously below the processing bandwidth of the whole storage within a predetermined time, priority levels set to LUs of which the input/output processing amount arrives at a bandwidth limit and the like are raised by one. By raising the priority levels of the LUs and the like by one, the bandwidth limits of the LUs and the like are changed to be high. Accordingly, the performance of the LU and the like is adjusted, and a change in the load status can be responded.
[Patent Document 1] Japanese Laid-open Patent Publication No. 2006-53601
[Patent Document 2] Japanese Laid-open Patent Publication No. 2009-93636
[Patent Document 3] Japanese Laid-open Patent Publication No. 2013-127758
However, according to the above-described QoS function, in a case where the performance of the storage apparatus that is requested from the host changes, the performance adjustment (flexibility of bandwidth, bandwidth accommodation) between resources (for example, LUs) inside the storage apparatus is difficult to be performed in accordance with the change in the performance according to the circumstances.
While technologies for responding to change in the load status by changing the priority level as described above are known, in a case where the performance is adjusted by changing the priority level, there are cases where a change interval of the bandwidth limit before and after the change of the priority level is extremely large. When the change interval of the bandwidth limit is large, the adjustment range according to raising/lowering the priority level is limited, and a change in the performance requested from the host is difficult to be delicately followed, and there are also cases where the processing bandwidth of the storage apparatus is degraded.